Re: [DNA] Re: RS/RA Exchange

[Brian Haberman <brian@innovationslab.net>]

Hi Greg,

Greg Daley wrote:

> Hi Brian,
> 
> Brian Haberman wrote:
> 
>>
>>
>> Erik Nordmark wrote:
>>
>>>> I'd guess that the ordering and selection issue is a generic one.
>>>> It would be good if we didn't re-invent solutions.
>>>
>>>
>>>
>>>
>>> There are protocols, like MLD and routing protocols, which elect some
>>> form of designated node (querier for MLD) but those protocols don't 
>>> produce
>>> a full sorted list of all the routers on the link.
>>> I wonder if there is something here which could be reused.
>>
>>
>>
>> So, I can dust off some "historic" code for this.  DVMRP has a HELLO
>> message like many other routing protocols.  But, DVMRP uses them to
>> announce reachability and discovery.  That is, peer routers on a link
>> look in the other routers' HELLO messages for their own addresses.
>> This allows them to determine when they have been "discovered" by
>> their peers.
> 
> 
> This sounds interesting as allows bidirectional checks that the
> router believes in the presence of the peer.

Yes.

> 
> This means that at least the discovery mechanism is assured.
> If we can do this based on existing message exchanges or
> mechanisms (or code :) that would be good though.

How about an RA option that lists all "learned" peers?

> 
>> Could we mimic this and have some type of announcement message that
>> a router would send out with all the other routers' addresses that
>> it has heard from?
> 
> 
> I thought that there was some work going on on
> a routing protocol agnostic 'hello' mechanism.
> 

The agnostic HELLO work is meant to have fast (re: millisecond)
detection of neighbor loss.  One proposal is PLP, there was one
a few years back called FLIPP.  Not sure if that is really the
model we want here.

> If there is it may make sense to re-use
> this, since the identifiers and priorities exchanged
> for routing would already have to be configured for
> routing protocol use.
> 
> I'd guess that this would be possible in the further
> future, but security mappings between routers
> may be difficult to achieve unless under single
> administration.


Regards,
Brian